"He who fears he will suffer, already suffers what he fears." Montaigne, that wise old 15th century philosopher, enlightened my life with this thought. In other words, if you keep worrying you're gonna drop your ice cream cone, you will.
If we think we will fail, we unconsciously do things to make our thoughts come true. Even knowing that, it's so hard to get rid of those pesky damning thoughts...kind of like trying not to think of the color blue when someone tells you not to think of the color blue.